A blood pressure is one type of index for analyzing a circulatory disease. Performing risk analysis based on the blood pressure is effective in preventing cardiovascular related disease such as apoplexy, cardiac arrest, and cardiac infarction. Conventionally, a diagnosis for performing the risk analysis is made from the blood pressure (occasional blood pressure) measured in medical institutions at the time of hospital visits and checkups. However, it is recognized from recent research that the blood pressure (home blood pressure) measured at home is more useful in diagnosing the circulatory disease than the occasional blood pressure. Accompanied therewith, the sphygmomanometer used at home is being widely used.
Most of the electronic sphygmomanometers currently being widely used use the blood pressure calculation algorithm of the oscillometric method or the microphone method.
In the oscillometric method, the change in arterial volume that occurs when the cuff pressure is pressurized up to a predetermined pressure (e.g., systolic blood pressure+30 mmHg) and then gradually depressurized at a predetermined speed (depressurization rate) is detected as a pressure pulse wave amplitude, and a predetermined algorithm is applied on the change in the pressure pulse wave amplitude to calculate a blood pressure value. The change in arterial volume that occurs when gradually pressurizing the cuff pressure at a predetermined speed (pressurization rate) may be detected as a pressure pulse wave amplitude, and a predetermined algorithm may be applied on the change in the pressure pulse wave amplitude to calculate a blood pressure value.
In the microphone method, the occurrence, attenuation, and disappearance of a Korotkoff sound that occurs when the cuff pressure is pressurized up to a predetermined pressure (e.g., systolic blood pressure+30 mmHg), and then gradually depressurized at a predetermined speed (depressurization rate) are detected with a microphone arranged in the cuff to determine the systolic blood pressure and the diastolic blood pressure.
In either blood pressure calculation method, the depressurization rate and the pressurization rate need to be set such that information on the pressure pulse wave amplitude or the Kortkoff sound can be fully obtained.
Specifically, the depressurization rate or the pressurization rate needs to be set according to the pulse rate of a person to be measured. In current sphygmomanometers, with respect to the depressurization rate and the pressurization rate, methods such as
1. setting the depressurization rate or the pressurization rate (e.g., 4 mmHg/sec etc.) sufficiently slow so that the pressure pulse wave amplitude information or the Kortkoff sound can be fully obtained;
2. estimating at least one or more of the systolic blood pressure, the diastolic blood pressure, or the pulse rate during pressurization, and setting the depressurization rate most suitable for the person to be measured based on such information (see Patent Document 1); and
3. setting the depressurization rate based on the average value of the pulse rates up to the previous measurement (see Patent Document 2) are adopted.    Patent Document 1: Japanese Patent Publication No. 3149873    Patent Document 2: Japanese Unexamined Patent Publication No. 2005-185681